In this photo taken with a cell phone, steam billows out of a hole in the asphalt on 41st St. between 3rd and Lexingon Avenues Wednesday afternoon, July 18, 2007. The New York Police Department said a... (Associated Press)

(Newser)
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An explosion in a steam pipe under the street near Grand Central Station at rush hour today gave New Yorkers a case of nerves, sending a guyer of steam many stories into the air and spattering onlookers with mud. The police department hastened to confirm that it was not terrorism related.

Grand Central was emptied—some commuters breaking into a run—and train service was interrupted. One employee at a nearby office building reported feeling the building shake, and hurrying down 30 flights of stairs. The explosion was said to be caused by something called a "water hammer," the result of condensation inside pipes.